An example of a device for the stuffer box crimping of a multifilament yarn is disclosed in EP 0 554 642 A1 and corresponding U.S. Pat. No. 5,351,374. The device comprises a conveying nozzle and a stuffer box arranged downstream from the conveying nozzle. The yarn is conveyed by means of the conveying nozzle into the stuffer box, compressed to a yarn plug and thereby stuffer box crimped. The conveying nozzle is loaded with a conveying medium, preferably a hot gas, which conveys the yarn within the yarn channel to the stuffer box. The yarn plug is formed inside the stuffer box. In doing so, the multifilament yarn deposits itself in loops on the surface of the yarn plug and is compressed by the conveying medium, which can discharge above the yarn plug out of the stuffer box. To do so, the chamber wall of the stuffer box comprises several slot-shaped openings on the perimeter through which the conveying medium can escape. In order to obtain uniform crimping of the yarn, plug formation must result with very high uniformity in the stuffer box. Thus, the friction forces caused by the relative motion of the yarn plug in the stuffer box have a substantial impact on the texturizing process. A counterbalance of forces exists between the conveying effect, or the dynamic pressure effect of the conveying medium flowing from the yarn channel of the conveying nozzle, and the braking action resulting from the friction forces on the yarn plug. Adjusting the conveying pressure, or adjusting additional suction of the conveying medium, essentially determines the conveying effect. In contrast, the braking action resulting from the friction between the yarn plug and the chamber wall essentially depends on the condition of the chamber wall.
In the device disclosed in EP 0 554 642 A1, only a slight number of friction surfaces exist due to the slot-shaped openings especially in the section with the gas-permeable wall. Therefore, wear marks are unavoidable in prolonged operation, which results in a change in the braking action. If the braking action decreases sufficiently, the yarn plug will be conveyed out of the stuffer box due to small frictional forces. The texturizing process then fails. On the other hand, as frictional forces increase, the yarn plug is no longer or no longer uniformly conveyed out of the stuffer box. Non-uniform stuffer box crimping occurs when a stick-slip effect begins in the stuffer box. These effects cannot be controlled with a dynamic medium opposing the conveying medium.
In contrast, one task of the present invention is to further improve a stuffer box crimping device for synthetic multifilament yarn in such a manner that uniform crimping is ensured in the yarn, even during very prolonged operation.